Catheters are placed at various locations within a patient for a wide variety of purposes and medical procedures. For example only, one type of catheter is a balloon dilatation catheter which is used in the treatment of a vascular stenosis. Such a catheter has a balloon at its distal end which is intended to be placed, in a deflated condition, within the stenosis, and then inflated while in the stenosis to expand radially the stenosed lumen of the blood vessel. Typically, the placement of such catheters involves the use of a guidewire which may be advanced through the patient's vasculature to the location which is to be treated. The catheter, which has a lumen adapted to receive the guidewire, is advanced over the wire which guides the catheter to the location to be treated. In so-called over-the-wire catheters, the guidewire lumen extends the entire length of the catheter and the guidewire received therein is entirely within the catheter except for the guidewire ends which extend from the distal and proximal ends of the catheter.
While over-the-wire catheters have many advantages traceable to a full-length guidewire lumen, including good stiffness and pushability and the availability of the guidewire lumen for pressure measurement and distal dye injections, such catheters do suffer some shortcomings.
For example, it is generally necessary for the guidewire and catheter to be advanced together through the guiding catheter and patient. Specifically, if the guidewire is first located across the stenosis and then the distal end of the catheter is threaded onto the proximal end of the guidewire, the physician would be unable to advance the catheter without undesirably also advancing the guidewire. That results because, unless an extension wire which can be twice the length of the catheter, is used, there is no portion of the guidewire extending out of the catheter that can be secured to ensure that only the catheter moves distally. Requiring the user to advance the catheter and guidewire together through the guiding catheter is undesirable because if it turns out that the user is not able ultimately to cross the stenosis with the guidewire, then the dilatation procedure will have to be aborted, resulting in the waste of a relatively expensive catheter.
Additionally, it often becomes necessary, in the performance of a catheter procedure, to exchange the indwelling catheter for another catheter, for example, for a catheter having a different size balloon. In one type of over-the-wire catheter exchange, the guidewire first is removed from the lumen of the indwelling catheter. Then a longer exchange wire is passed through the catheter to replace the original wire. Then, while holding the exchange wire by its proximal end to maintain it in place, the catheter is withdrawn proximally from the blood vessel over the exchange wire. After the first catheter has been removed, the next catheter is then threaded onto the proximal end of the exchange wire and is advanced along the exchange wire and through the patient's blood vessels until the distal end of the catheter is located as desired. The exchange wire may be permitted to remain in place or may be exchanged for a shorter, conventional length guidewire.
A non-over-the-wire catheter that permits the guidewire to be fully inserted into the patient before the catheter, and also permits catheter exchange while maintaining the in-situ guidewire in place is the so-called MONORAIL.TM. type catheter. Catheters of this type, which are described in U.S. Pat. Nos. B1 4,762,169, 5,040,548 and 5,061,273, are formed so that the guidewire is located outside of the catheter except for a short segment at the distal end of the catheter, which passes over the wire. The distal segment of the catheter has a short lumen which extends from the distal tip of the catheter to a more proximally located opening near the distal tip. In use, the guidewire is placed initially in the patient's vascular system. The distal segment of the catheter then is threaded onto the wire. The catheter can be advanced alongside the wire with its distal segment being attached to and guided along the wire. The catheter can be removed and exchanged for another catheter without the use of the usual double length exchange wire and without requiring withdrawal of the initially placed guidewire.
Although the proposed MONORAIL catheter system may avoid the requirement for using a long exchange wire, it presents several difficulties. For example, it is not possible to exchange guidewires in an indwelling catheter as can be done with over-the-wire catheters. Additionally, the device presents a potential for damaging the delicate inner surface of an artery from a tension load applied to the guidewire which would tend to straighten the artery. Also, there is an increased risk of guidewire entanglement in those procedures where multiple guidewires are used, because the guidewires are exposed within the blood vessel.
The MONORAIL catheters, which do not include a guidewire lumen for the entire length of the catheter, also lack the desired stiffness and pushability for readily advancing the catheter through tortuous blood vessels. In addition, the lack of a full length guidewire lumen deprives the physician of an additional lumen that may be used for other purposes, e.g., pressure measurement and distal dye injection.
It is among the general objects of the invention to provide an improved device which overcomes the foregoing difficulties.